After the investigators have received informed consent from the parents/guardians, blood samples 0.2 ml from the child will be taken according to present clinical practice at if possible from cord (2ml) and at days 0, 7, 14, 28 and in postmenstrual weeks 32, 36 and 40. Blood samples from the mothers for Fatty Acids analyses will be taken after birth, day 7 and at gestational weeks 36 and 40. At the same time (except from day 1), breast milk samples are taken. Length in cm, weight in gram and head circumference in cm are measured weekly.